1. Field of the Invention
This invention relates generally to the field of control systems and, more particularly, to multilevel, multi-input combinational logic control systems using a serial multiplex bus.
2. Description of the Related Art Including Information Disclosed Under 37 CFR 1.97-1.99
Control systems employing a time-division serial multiplex bus for controlling at least one output device by a plurality of input devices are well known. An example is shown and described in U.S. Pat. No. 4,808,994 issued Feb. 28, 1989, to Riley which is incorporated by reference into this application. Such known control systems use the bus as a wired-OR and use control modules with logical circuits associated with each input and each output device. It is also well known in such control systems for a plurality of the input devices to act together in a preselected combinational scheme to control one or more output devices. Such combinational schemes are representable by means of Boolean algebra and are illustratable by means of interconnections of four basic logic operations or logic gates: AND, OR, NOR, and NAND gates. The electronic activation of selected inverter circuits associated with the inputs and outputs of the control modules allow the wired-OR of the bus to selectively function equivalently as any one of the four logical operations.
In control systems using a serial multiplex bus, simultaneous connection to the bus of a plurality of input devices via control modules yields a single logic stage output logically responsive to the inputs. In known control systems, integrated, two-channel control modules are provided with an internal logical gate connection between an output of each channel to produce a third output to form a second logic stage, or level of combinational logic. This third output in known systems is used only to drive an output device directly without connecting the second stage output to the bus.
In known control systems more than two stages of combinational logic are only obtained by using a host computer or by using more than one bus or multiple nonbus connections. The use of a host computer, more than one bus or multiple nonbus connections defeats the purpose of a single bus control system and disadvantageously adds cost and complexity.